Alkylation of aromatic amines



Patented Mar. 19, 1935 UNITED S A'i'hl'i' OFFICE ALKYLATIION 0F AROMATICAItflNES No Drawing.

Application December 12, 1931,

Serial No. 580,732

17 Claims.

This invention relates in general to the alkylation of aromatic amines,and particularly to the alkylation of primary aromatic amines when thealkyl groups to be introduced into the amine contain more than onecarbon atom. More particularly, the invention relates to the ethylationof aniline and its homologues.

It is Well known that by a process of alkylation, alkyl radicals may besubstituted for one or both of the hydrogens in the amino group of aprimary aromatic amine. With an alkyl radical such as the methyl group,this substitution takes place quite readily. For example, aniline whenheated with methanol and a relatively small amount of sulfuric acid,under elevated temperature and pressure may be converted substantiallycompletely to dimethylaniline or mixtures thereof withmonomethylaniline. However, if an alkyl alcohol of higher order thanmethyl is used, this procedure is unsatisfactory because of sidereactions and for other reasons. To a greater or less extent, otherdisadvantages have attended previously proposed methods for alkylatingaromatic amines to a higher order than methyl. Thus, in some processesheretofore proposed for ethylating aniline, mixtures of monoanddiethylaniline and unconverted aniline have been obtained. In orderto'be commercially feasible, such processes customarily involve removalor recovery of the unconverted aniline, which adds to the cost ofproduction and, in general, leaves much to be desired.

Our invention has as one of its objects a new and improved method ofallzylating primary aromatic amines, particularly as regards alkylationsof aniline or its homologues to a higher order than methyl, wherebymixtures of the monoand dialkyl substituted amines are obtained. A further object of the invention is the provision of a flexible process forregulating the proportions of monoand disubstituted amines produced. Astill further object is the ethylation of aniline to producesubstantially binary mixtures of monoand diethylaniline by a methodwhich is controllable to such an extent that a relatively small changein the conditions of ethylation will cause a marked difference in theratio of monoand diethylaniline produced, and the amount of each productcan be varied as needed. An additional object of the invention is theprovision of a method for ethylating primary aromatic amines which isbetter from the economic standpoint than any method previously proposed.Other objects and advantages of the invention will be apparent byreference to the following description thereof.

In its broader aspects, the invention comprises producing monoanddialkyl aromatic amines by reacting a primary aromatic amine with analkyl alcohol, preferably of a higher order than methyl, and thecorresponding allcyl chloride under elevated pressure and temperature.The resultant product contains an oily mixture of monoand dialkylaromatic amines, which may be recovered in any suitable manner, forexample, by making the reaction product alkaline, whereupon the oilseparates from the remainder of the liquid and may be removed by meansof a conical separator or by any other convenient method. The oilymixture may be used as such in certain chemical processes. Or, ifdesired, the monoand dialkyl amines may be separated from each other byany suitable means, for instance, by fractional distillation or byfractional crystallization of salts of the amines.

The invention may be well illustrated by the ethylationof aniline. Thisis preferably accomplished by reacting aniline, ethyl alcohol, and ethylchloride, under autogenous pressure and at an elevated temperature,while regulating the proportions of the reactants and more particularlythe amount of ethyl chloride to produce a product containing a mixtureof monoand diethylaniline in desired ratios, substantially nounconverted aniline being present. The resultant mixture may berecovered in any suitable manner and the two constituents separated orused as such without the difficulties and expense involved when asubstantial amount of unconverted aniline is present. We have found thisprocess to be exceptionally advantageous on a plant scale because of itsflexibility.

While the invention is susceptible of considerable variation in themanner of its practical application, particularly as regards conditionsof time, temperature, pressure and proportions of reactants used, thefollowing examples Will illustrate how it may be practised.

Example I oil layer separated by meansof a conical separator. The oilcontained approximately monoethylaniline and 40% diethylaniline.

Example II The reaction described in Example I was effected with 242parts by weight of ethyl chloride instead of 208 parts, all otherproportions of reactants and conditions of time and temperatureremaining the same. The autogenous pressure in this case was about200-250 pounds per square inch. The oil was recovered as usual andanalyzed approximately 35% monoethylaniline and diethylaniline.

Example I]! Example I Example II Example III Time of heating (hrs.) 5 55 Temperature 0.- 180-185 180-185 180-185 Pressure lbs/sq.

(approximate) Y 175225 200-250 300-360 Ratio moles ethyl alcohol permole of aniline- 1.09 1. 00 2. 46 Ratio moles of ethyl I chloride permole of aniline 1. 0. 645 0. 0. Percent monoethylaniline in oil produced60.0 35. 0 12. 5 Percent diethylaniline in oil produced 40. 0 65.0 87. 5

It will be seen in the above table that a change of about 0.10 moles ofethyl chloride per mole of aniline, all other conditions remaining thesame approximately reverses the proportions of monoand diethylanilineproduced. Since the demand for each of the products varies from time totime, the advantage of being able to modify the process to meet thedemand as it arises is obvious. This has heretofore been possible onlyto a much more limited extent.

We wish it to be understood that the above examples are not meant tolimit the scope of the invention. Instead of aniline, we may alkylatethe homologues thereof, e. g. the toluidines, ,(metatoluidine, etc.) andXylidines, or any other primary aromatic amines such as thenaphthylamines. The exact conditions of operation, of course, willdepend upon the nature of the amine treated. In general, conditionssubject to variation are the temperature, the time and the pressure ofthe reaction and the proportions of the reactants.

The temperature may vary within relatively wide limits, but, generallyspeaking, should be so regulated as to avoid ring alkylation at thehigher temperatures and a low rate of alkylation at the lowertemperatures. In ethylating anilineor its homologues, we prefer toemploy temperatures within the range of -190 C. and preferably HBO- C.For the ethylation of naphthylamines, temperatures below about 130 C.are preferable.

The time allowedfor the reaction to take place appears to be afunctionof the temperature em-- ployed. If the temperature used isrelatively low, a longer period of heating is required than in caseswhere the reaction is carried out at relatively high temperatures.

In practicing our invention we prefer to heat the reactants in a closedvessel so that the pressure of the reaction is the autogenous pressureproduced by the reaction mixture. According to this method of procedurethe pressure is largely a function of the temperature and theproportions of amine, alkyl alcohol, and alkyl chloride used. Ifdesired, however, other sources of pressure may be employed such as, forexample, the introduction of a compressed gas or vapor which is inert tothe reactants or does not affect the reaction unfavorably. Elevatedpressures tend to favor the production of alkyl aromatic amines by ourprocess and pressures varying from slightly super-atmospheric to 1000atmospheres are contemplated. As a general rule, it is preferable toemploy pressures within the range of about 10-1'00 atmospheres. Inethylating aniline pressures within the range of about 1030 atmosphereshave. given especially desirable results. I i

The proportions of the various reactants employed to produce monoanddialkyl substituted aromatic amines in accordance with our inventiondepend largely upon the ratio of monoto dialkyl amines desired. Thus,within a certain range, other things being equal, a small increase inthe amount of alkyl chloride present in the reaction mixture willincrease the proportion of dialkylamine formed. In general, it ispreferable that the amount of alkyl chloride used should fall within therange of about 0.6-1.0mole per mole of primary aromatic amine. The useof such small alkyl chloride concentrations is a distinctive feature ofthe invention and a decided advantage from the economic viewpoint.

The proportions of alkyl alcohol employed may vary within relativelywide limits but, generally speaking, should not be. less than about onemole er mole of primary aromatic amine treated.

As previously indicated, the alkyl chloride used in effectingalkylations by our process should correspond to the alkyl alcoholemployed, or vice versa. That is to say, the alkyl chloride and alkylalcohol should contain the same number of carbon atoms similarlygrouped. Otherwise; complex mixtures of alkylated amines may result. Byalkyl we mean-a radicalderived from anacyclic hydrocarbon by theelimination of one atom: of hydrogen, such as, for example, propyl,isopropyl, allyl, butyl, isobutyl, etc.

In describing our invention, we, have referred to the production ofmixed monoand. dialkyl aromatic amines, and particularly ethylatedaniline and homologues thereof, which contain substantially nounconverted primary amine. In actual practise, it is difiicult todetermine the amount of primaryaromatic amine in mixtures of monoanddialkyl aromatic amines when less than about 1% of the primary amine ispresent. By substantially no unconverted primary aromatic amine,therefore, we mean less-than'about 1% by weight. I I

We have found that the present inventionobviates many of thedifiiculties formerly attending large scale alkylationsof a higher orderthan. methyl, and particularly ethylations; that eth ylated products ofthe character herein described can be produced more cheaplyby 5 ourprocess than byany previously proposed method, and, in general,- theinvention represents an advancement of "the-art".

As many apparent and widely different embodiments of this invention maybe made without departing from the spirit thereof, it is to beunderstood that we do not limit ourselves to the foregoing examples ordescription except as indicated in the following claims.

We claim:

1. In a process of producing mono and dialkyl aromatic amines the stepwhich comprises reacting a primary non-phenolic aromatic amine with analkyl alcohol and the corresponding alkyl chloride undersuper-atmospheric pressure, the proportions of alkyl chloride used beingwithin the range of 0.6 to 1.0 mole per mole of primary aromatic amine.

2. In a process of producing monoand diethyl aromatic amines the stepwhich comprises reacting a primary non-phenolic aromatic amine withethyl alcohol and ethyl chloride under superatmospheric pressure.

3. In a process of producing monoand diethyl aromatic amines the stepwhich comprises reacting a primary non-phenolic aromatic amine withethyl alcohol and ethyl chloride under superatmospheric pressure, theproportion of ethyl chloride used being within the range of 0.6 to 1.0mole per mole of primary aromatic amine.

4. In a process of producing monoand diethyl aromatic amines of thebenzene series the step which comprises reacting a non-phenolic primaryaromatic amine of the benzene series with ethyl alcohol and ethylchloride under super-atmospheric pressure.

5. In a process of producing monoand diethyl aniline the step whichcomprises reacting aniline with ethyl alcohol and ethyl chloride undersuperatmospheric pressure.

6. In a process of producing monoand diethyl aniline the step whichcomprises reacting aniline with ethyl alcohol and ethyl chloride undersuperatmospheric pressure, the proportions of ethyl chloride used beingwithin the range of 0.6 to 1.0 mole per mole of aniline.

7. The process of producing monoand diethylaniline which comprisesreacting aniline with ethyl alcohol and ethyl chloride undersuperatmospheric pressure and at a temperature within the range of aboutto about 190 C.

8. The process of producing monoand diethylaniline which comprisesreacting aniline with ethyl alcohol and 0.6 to 1.0 mole of ethylchloride per mole of aniline, under super-atmospheric pressure and at atemperature within the range of about 160 to about 190 C.

9. The process of producing monoand diethylaniline which comprisesreacting together in a closed vessel aniline, ethyl alcohol, and ethylchloride in proportions corresponding to at least one mole of ethylalcohol per mole of aniline, and 0.6 to 1.0 mole of ethyl chloride permole of aniline, under autogenous pressure and at a temperature of to C.

10. The process of ethylating aniline which comprises reacting togetheraniline, ethyl alcohol, and ethyl chloride in proportions correspondingto at least one mole of ethyl alcohol per mole of aniline, and 0.6 to1.0 mole of ethyl chloride per mole of aniline, under super-atmosphericpressure and at a temperature of 180 to 185 C., to produce a productcontaining a mixture of monoand diethylaniline but substantially nounconverted aniline, and separating said mixture of monoanddiethylaniline from said product.

11. In a process of producing monoand diethyl aniline the step whichcomprises reacting aniline with ethyl alcohol and ethyl chloride under asuper-atmospheric pressure within the range of about 10 to about 30atmospheres.

12. In a process involving replacing by an alkyl radical the hydrogen ofan amino group of a non-phenolic aromatic amine, the step whichcomprises reacting said aromatic amine with an alkyl alcohol and thecorresponding alkyl chloride under super-atmospheric pressure.

13. In a process involving replacing by an alkyl radical the hydrogen ofan amino group of a non-phenolic aromatic amine which may contain alkylsubstituents in the aromatic ring, the step which comprises reactingsaid aromatic amine with an alkyl alcohol and the corresponding alkylchloride under super-atmospheric pressure.

14. In a process involving replacing by an alkyl radical the hydrogen ofan amino group of an aromatic amine selected from the group consistingof aniline and homologues thereof, the step which comprises reactingsaid aromatic amine with an alkyl alcohol and the corresponding alkylchloride under super-atmospheric pressure.

15. In a process involving replacing by an alkyl radical the hydrogen ofan amino group of a nonphenolic aromatic amine which may contain alkylsubstituents in the aromatic ring, the step which comprises heating saidaromatic amine with an alkyl alcohol and the corresponding alkylchloride under super-atmospheric pressure at an alkylation temperaturebelow that giving rise to substantial ring alkylation of the amine.

16. In a process involving replacing by an alkyl radical the hydrogen ofan amino group of a nonphenolic naphthyl amine, the step which com- PAULWHI'I'IIER CARLETON. JOSEPH DONALD WOODWARD.

